1. Field of the Invention
The present invention relates to projection type display devices such as a projector, and particularly to a projection type display device using a plurality of light sources and provided with a cooling system that can cool the light sources adequately.
2. Description of Related Art
A projection type display device such as a projector has been known as a device for obtaining an image on a big screen. The projection type display device modulates light from a light source lamp with a video signal so as to form an optical image and radiates, by using an image display device such as DMD (Digital Micromirror Device) or a liquid crystal, thereby projecting the optical image in a magnified manner on the screen by the use of a projection lens.
The light source lamp is filled with mercury, a rare gas, a metal halide and the like. When a predetermined voltage is applied to the electrode in the light source lamp, a discharge arc occurs and the filler gas inside the lamp is convected. The discharge arc is curved to form an arc due to the convection of the filling gas, approaches the top of the light source lamp, and thus the temperature of the light source lamp rises. If the temperature of the light source lamp rises extremely, problems such as whitening and life property degradation will occur. To the contrary, when the temperature of the light source lamp is extremely low, it causes problems such as blacking and degradation in the brightness of the light source. Therefore, temperature management of the light source has a great influence on the quality and reliability of the projection type display device.
In particular, for a device that uses a plurality of light sources for the purpose of providing a projected image with high brightness (see JP 3581568 and JP 2000-171901 A for example), temperature management of the light source is important. Namely, a device that uses a plurality of light sources has an advantage in that even when any one of the light sources has a problem that causes a failure in lighting, the image projection will not be discontinued if the remaining light source is kept lightened. On the other hand, the conditions for lighting the light sources will be complicated. In such a case, it is particularly important to manage the temperature of light sources in relation to the direction in which the device is installed. With regard to this, however, conventionally, there has been only a disclosure of an investigation of the efficiency of a cooling fan concerning a device provided with a single light source installed in certain limited directions (see JP H10-106307 A for example).
However, as the uses of projection type display devices including a plurality of light sources have increased, the installation conditions have become diversified, and as a result, there is a high possibility that the devices are installed in a variety of postures. Light source lamps need to be maintained within a predetermined temperature range (e.g., 900° C. to 1,150° C.) in order to ensure their performance, and in recent years, appropriate temperature management of the light sources conforming to a variety of installation conditions has been required. Particularly, when light source lamps generate heat, the temperature inside the light source unit on the upper side (direction opposite to gravity) rises due to the convection of air. Consequently, the temperature distribution inside the light source unit changes in a variety of ways as a result of variations in the installation posture of the device. Therefore, it is not possible to handle the change in the temperature distribution inside the light source unit by uniformly supplying cool air to the light sources unit from a cooling fan through certain air outlets, so that the cooling efficiency declines. As a result, maintaining the temperature of the light sources within a desired range becomes difficult and the possibility of a breakdown increases. To prevent this problem, it is necessary to increase the scale of the cooling system, which results in an increase in the size of the device and in a problem in terms of cost.